Optical disc, optical disc device, and method for recording an optical disc

ABSTRACT

In an optical disc, a sector is sequentially formed with a first gap field, a first guard data recording field, a data recording field composed of synchronous signal and user data, a second guard data recording field, and a second gap field, wherein the length of the first and second gap fields, and the length of the first and second guard data recording fields is changed randomly in every recording, and the changing amount of the first and second guard data recording fields is set smaller than the changing amount of the first and second guard data recording fields, thereby suppressing optical disc medium deterioration in every sector and every mark resulting from repeated recording.

This is a Continuation of application Ser. No. 08/946,576 filed Oct. 7,1997 now U.S. Pat. No. 6,034,932.

FIELD OF THE INVENTION

The present invention relates to an optical disc for recording andreproducing digital signals in a sector unit of an optical disc, anoptical disc device, and a recording method for an optical disc.

DESCRIPTION OF THE PRIOR ART

Optical discs are presently widely distributed as read-only recordingmedia for audio and video use, e.g., a compact disc (CD), and asrewritable recording media, e.g., a mini disc (MD). Moreover, as anexternal memory device for a computer, rewritable 3.5-inchmagneto-optical discs and 5-inch phase change optical discs (PD) arebecoming popular.

Henceforth, as the recording media for multimedia, digital video disc(DVD) using phase change optical discs is about to be popularlymarketed. One of the merits of the phase change optical disc is that tooverwrite an information signal, only a single laser beam is necessaryas a recording means. That is, when a modulated laser output is emittedonto a recorded information track as a function of an information signalswitching between a recording level and an erasing level, a new signalcan be recorded while erasing an existing information signal.

A format structure of such an optical disc is explained by referring toFIG. 18. In FIG. 18, reference numeral 1 is an optical disc, 2represents tracks on the optical disc 1, and 3 designates sectorsdividing the tracks into plural fields. Each sector 3 dividing thetracks into plural fields. Each sector 3 is composed of a header field 4including track and sector address information, a gap field 7 with nosignal recorded therein, a data recording field 5 for recording userdata, and a buffer field 6 for absorbing the effects of imprecision inrotation of the motor.

The header field 4 is usually formed of prepits, and is not used forrecording. Reference numeral 4a is a synchronous signal VFO forsynchronizing, 4b is an address mark for detecting the header field by aspecial recording pattern not appearing on the modulation pattern, 4c isa field containing a physical identification address (PID) havingaddress information with respect to a physical position of the sector,and 4d is an ID error detection (IED) for detecting an address error.The header field composed of blocks 4a to 4d may be composed of pluralheader fields in order to enhance the reliability thereof.

The data recording field 5 is composed of a synchronous signal VFO 5bfor synchronizing and user data 5c.

Referring now to FIG. 19, an optical disc device for recording andreproducing signals by a recordable optical disc is explained. In FIG.19, reference numeral 1 is an optical disc, 10 is an optical head forrecording and reproducing signals on tracks of the optical disc 1, 11 isa servo control circuit for focusing an optical beam of a semiconductorlaser on the tracks of the optical disc, 12 is a laser driving circuitfor controlling the optical output of the semiconductor laser, 13 is adata modulation circuit for digitally modulating coded data into a formsuited to recording, and 14 is a VFO generating circuit for generatingVFO as a synchronous signal. Reference numeral 15 is a coding circuitfor performing error correction coding on recorded data, 16 is a recordcontrol circuit for controlling the timing of recording, 17 is anaddress detecting circuit for detecting an address signal from areproduced signal, 18 is a system control circuit for controlling theoperation of the entire optical disc device composed of amicroprocessor, and other related circuitry, and 19 is data to berecorded.

The data coded in the coding circuit 15 is modulated in the datamodulation circuit 13 and is output as modulated data. The synchronoussignal VFO generated in the VFO generating circuit 14 is added to thebeginning of this modulated data and is delivered to the laser drivingcircuit 12, and is recorded in the optical disc 1.

In such a rewritable light-operative optical disc, however, the numberof recording repetitions is limited, since the recording mediumdeteriorates due to thermal load, under repeated exposure to light.Generally, such deterioration phenomena tend to be more prevalent in thedeterioration area as the number of recording repetitions increases.Deterioration phenomena may be roughly classified into two types asfollows:

(1) deterioration phenomenon in each sector, occurring in the beginningend (record start position) of a recording field in the sector andterminating end (record end portion), by repeated recording on thesector, and

(2) deterioration phenomenon in each mark, occurring in the mark area,as the mark row of a same pattern is recorded repeatedly in the sameposition in the sector.

First, in the deterioration phenomenon in each sector, as recording isrepeated, deterioration gradually occurs in the recording foil in thebeginning end and terminating end of a recording field in the sector,and this defect expands backward of the sector from the beginning end(to the relative laser advancing direction on the optical disc) andforward of the sector from the terminating end (to the reverse directionof the relative laser advancing direction on the optical disc).

The above-described phenomenon is understood to occur because, when therecording foil is in a fused state, a movement phenomenon of therecording foil substance in the track direction occurs. For instance, bythe movement of the recording foil substance to the sector forwarddirection, as fusion and solidification are repeated multiple times, therecording foil substance accumulates in the record start point portionwhere the thermal load to the recording foil changes suddenly, and therecording foil substance is decreased in thickness at the recording endpoint portion. As a result, the film thickness becomes uneven betweenthe recording start point and end point, and thermal or opticalcharacteristics deteriorate, the film exfoliates, and/or the quality ofreproduced signals deteriorates in the data beginning end or terminatingend, thereby impeding correct recording and reproducing of information.

Next, in the deterioration phenomenon in each mark, as the recording isrepeated, a defect occurs in the recording foil when recording the samepattern, and this defect expands forward and backward of the markportion.

That is, when the same data is repeatedly recorded in the same sector,fusion and solidification are repeated multiple times in some areas,while other areas are not fused at all.

Generally, when rewriting the recorded data in an optical disc, the datais rewritten in the sector unit. Therefore, if information is changed inpart of a sector, the entire sector is rewritten. In a TOC (Table ofContents) field or a directory field where information corresponding tothe table of contents of the recorded information in the disc isrecorded, in particular, similar data are often recorded repeatedly, andthe rewriting frequency is high. In the ordinary data sector, too, samedata is recorded repeatedly in the synchronous signal portion VFO or thelike, and the aforementioned kind of deterioration phenomenon occurs insuch instances. As a result, the film thickness of the recorded filmfluctuates in the boundary region of the portion fused and solidifiedrepeatedly and the portion not fused at all, and thus the thermal andoptical characteristics deteriorate, and the quality of reproducedsignal in this portion deteriorates, thereby blocking normal recordingand reproducing of information.

OBJECT AND SUMMARY OF THE INVENTION

The present invention is directed, in the light of the above describedproblems, to an optical disc for recording and reproducing data in theunit of sectors. It is an object of the invention to provide an opticaldisc capable of reducing the deterioration of the recording foil of theoptical disc in every sector and every mark derived from repeatedrecording, simplifying the associated signal processing system, andsuppressing effects of deterioration phenomena on accurate recording andreproducing of information, and an optical disc device, and a recordingmethod for an optical disc.

To achieve these and other objects, in a first feature of the opticaldisc of the invention, a header field including a sector identifyingsignal, and a data recording field including a synchronous signal areprovided in each one of plural sectors dividing the tracks, and a guarddata recording field for recording specific guard data is providedbetween the header field and data recording field.

In a second feature of the optical disc of the invention, the guard datain the guard data recording field is the same as the recording patternin the synchronous signal field, and the phase of the recording patternis continuous near the boundary of the guard data recording field andsynchronous signal field.

As a result, the guard data recording field can be substantiallyutilized as the synchronization signal field, and the lock-in range ofsynchronization can be expanded further than the synchronous signalfield, so that the stability of acquisition of synchronism can beimproved even in view of medium deterioration due to repeated recording.

In a third feature of the optical disc of the invention, the recordingsection of the guard data recording field is changed randomly in everyrecording.

As a result, the guard data recording field for recording identicalsignal patterns and the mark position recorded on the recording mediumby repeated recording is shifted randomly in every recording, so thatdeterioration of the recording medium can be prevented.

In a fourth feature of the optical disc of the invention, asector-structure is formed to comprise, sequentially, a first gap fieldhaving no signal, a first guard data recording field for recording guarddata, a data recording field including synchronous signal and user data,a second guard data recording field, and a second gap field, wherein thetotal length of the first and second gap fields is constant, the totallength of the first and second guard data recording fields is constant,and, in the sector, at the time of recording, the length of the firstgap field and the first guard data recording field is changed randomlyupon every recording, and the changing amount of the first gap field isset smaller than the changing amount of the first guard data recordingfield.

Accordingly, since the first and second gap fields and the first andsecond guard data recording fields change randomly upon every recording,the medium deterioration in every sector and in ever mark due torepeated recording can be suppressed.

In a fifth feature of the optical disc of the invention, in addition tothe fourth feature, the resolution of the changing amount of the firstgap field is a channel bit unit, and the resolution of the changingamount of the first guard data recording region is a byte unit.

Hence, while maintaining the ease of realization of data processing onthe signal processing system, the medium deterioration in every sectorand in every mark due to repeated recording can be suppressed.

In a sixth feature of the optical disc of the invention, in addition tothe fourth feature, the signal polarity of guard data and data recordingfield data is changed randomly upon every recording.

As a result, even in a limited random shift amount, the mediumdeterioration in every sector and in every mark can be suppressed.

The optical disc device of the invention comprises means for recordingand reproducing the optical discs as mentioned herein, and is capable ofsuppressing the medium deterioration in every sector or in every markdue to repeated recording.

The recording method for an optical disc of the invention comprises amethod of recording these optical discs, and is hence capable ofsuppressing the medium deterioration in every sector or in every markdue to repeated recording.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a format structure of an optical discaccording to a first embodiment of the invention.

FIGS. 2a-c show deterioration of the recording medium and synchronoussignal field VFO at the record start point when recorded repeatedly.

FIG. 3 is a block diagram of an optical disc device according to asecond embodiment of the invention for recording in and reproducing froman optical disc having a guard data recording field.

FIGS. 4a-d depict a synchronous signal section in which guard data in aguard data recording field has a pattern different from the synchronoussignal VFO.

FIGS. 5a-d show a synchronous signal section of an optical disc in athird embodiment in which guard data in a guard data recording field hasthe same pattern as the synchronous signal VFO.

FIG. 6 is a block diagram of an optical disc according to a fourthembodiment for recording and reproducing in which the recording patternin the guard data recording field is the same as the synchronous signalfield VFO.

FIG. 7 is a flowchart for explaining a recording method for an opticaldisc according to a fifth embodiment for recording and reproducing inwhich the recording pattern in the guard data recording field is thesame as the synchronous signal field VFO.

FIGS. 8a-d depict the conditions of sectors of an optical disc accordingto a sixth embodiment for changing randomly the sector recording sectionupon every recording.

FIG. 9 is a block diagram of an optical disc device according to aseventh embodiment for recording and reproducing a signal in an opticaldisc by changing randomly the sector recording section upon everyrecording.

FIG. 10 is a format of an optical disc for recording and reproducing byrandomly changing the recording section in first and second gap fieldsand first and second guard data recording fields, in every sector, uponevery recording.

FIG. 11 is a block diagram of an optical disc device according to aneighth embodiment for recording and reproducing by changing randomly therecording section in first and second gap fields and first and secondguard data recording fields, in every sector, upon every recording.

FIG. 12 is a block diagram showing an example of a second randomchanging circuit.

FIG. 13 is a flowchart for explaining a recording method of the opticaldisc according to the eighth embodiment.

FIGS. 14a-d depict the mode of the sector when randomly changing thefirst and second gap fields and first and second guard data recordingfields.

FIGS. 15a-b show the deterioration area of the sector when randomlychanging the first and second gap fields and first and second guard datarecording fields.

FIGS. 16a-c are diagrams for explaining the polarity of recording signaland the recording stage on an actual optical disc.

FIG. 17 is a graph of results of an experiment showing the effect ofrandom shift according to the invention.

FIG. 18 is a format of a conventional recordable optical disc.

FIG. 19 is a block diagram of a conventional recordable optical discdevice.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, embodiments of the invention aredescribed below.

Embodiment 1

FIG. 1 shows a format structure of an optical disc according to a firstembodiment of the invention. Explanation is omitted for the parts alsoshown in the format structure of FIG. 18 relating to the prior artdescribed above.

As compared with the prior art, the added and modified portion is aguard data recording field 100 for recording guard data, disposedbetween the header field 4 and data recording field 5. The guard datarecording field 100 is disposed behind the gap field 7 and immediatelybefore the data recording field 5. Since no signal is recorded in thegap field 7, recording of signals in the sector begins at the guard datarecording field 100.

Referring to FIGS. 2a-c, in the optical disc having the format structurein FIG. 1, the relation between deterioration of the recording medium atthe record start point and synchronous signal field VFO upon repeatedrecording is explained.

FIGS. 2a-c show the mode of deterioration of the recording medium nearthe record start point of the data recording field 5, in which FIG. 2ashows a single repetition only, FIG. 2b shows 50,000 repetitions, andFIG. 2c shows 100,000 repetitions.

In the initial stage of a single repetition in FIG. 2a, the guard datarecording field 100 at the start point of recording of the sector, isfree from medium deterioration, and thus there is no problem. Here, theinterval of the guard data recording field in the initial state issupposed to be T1, and the internal of the synchronous signal field VFOis supposed to be T2.

After 50,000 repetitions as shown in FIG. 2b, medium deteriorationoccurs and is indicated by 30 for an interval of TC1 at the beginning ofthe guard data recording field 100., the guard data recording field 100shortens to T4 by the interval TC1 of the length of the mediumdeterioration 30. However, if medium deterioration occurs, only theguard data recording field 100 in which guard data is recorded isshortened in length. The synchronous signal field VFO necessary forsynchronization is completely free from the effects of mediumdeterioration 30, and the synchronous interval T2 remains the same as inthe initial state. Hence, as in the initial state, stable acquisition ofsynchronism is realized.

After 100,000 repetitions as shown in FIG. 2c, the medium deterioration30 at the beginning of the guard data recording field 100 is extended tointerval TC2. As a result, the guard data recording field 100 shortensfurther to be T5. However, only the guard data recording field in whichguard data is recorded is shortened in length, and the synchronoussignal field VFO necessary for synchronization is completely free fromthe effects of the medium deterioration 30, and the synchronous intervalT2 likewise remains the same as in the initial state. Hence, as in theinitial state, stable acquisition of synchronism is realized.

As explained, according to the present embodiment, by providing theguard data recording field 100 for recording guard data between theheader field and the data recording field containing synchronous signal,the synchronous signal field is prevented from being shortened by themedium deterioration caused by repeated recording, so that theacquisition of synchronism is stabilized.

Embodiment 2

Referring now to FIG. 3, an optical disc device according to a secondembodiment of the invention which is intended to record and reproduce inan optical disc having a guard data recording field at the beginning ofa sector is described. Explanation is omitted for the parts alreadydiscussed in the optical disc device of FIG. 18 relating to the priorart described above.

What is added to the prior art is a guard data generating circuit 200and a first record control circuit 201. The guard data generatingcircuit 200 generates specified guard data. The guard data of the guarddata generating circuit 200 is first provided, synchronous signal VFO ofthe synchronous signal VFO generating circuit 14 is added next, and thenmodulated data of the data modulating circuit 13 is added later still.Such data timing is controlled by the first record control circuit 201.The combined guard data, synchronous signal VFO, and modulated data areprovided to the laser driving circuit 12, and is recorded on the opticaldisc.

According to the present embodiment, as described herein, in addition tothe conventional constitution of the optical disc device, the guard datagenerating circuit 200 for generating guard data and first recordcontrol device 201 are provided, and by recording the guard data in theguard data recording field 100 between the header field 4 and thesynchronous signal field VFO at the starting portion of the datarecording field 5, the synchronous signal is protected from mediumdeterioration caused by repeated recording, so that an optical discdevice stable in acquisition of synchronism is realized.

Embodiment 3

FIGS. 4a-d and FIGS. 5a-d show the relationship between thedeterioration of recording medium at the record start point uponrepeated recording and the synchronizing interval of synchronous signalfield VFO, in an optical disc having a format structure according to athird embodiment of the present invention. In the optical disc of thethird embodiment, the recording pattern of guard data in the guard datarecording field is the same as the recording pattern of the synchronoussignal field VFO. In the boundary of the guard data recording field andsynchronous signal field, moreover, the phase of the recording patternis matched so as not to cause discontinuation.

First, in FIGS. 4a-d, the guard data in the guard data recording fieldis different from the recording pattern of the synchronous signal fieldVFO. FIG. 4a shows the data recording field after one repetition, FIG.4b shows the lock-in range on synchronization, FIG. 4c shows the datarecording field after 100,000 times of repetition, and FIG. 4d shows thelock-in range on synchronization after 100,000 times of repetition.

In the initial state after one repetition, the guard data recordingfield 100 at the record start point of the data recording field 5 isfree from medium deterioration. The interval of the guard data recordingfield in the initial state is supposed to be T1, and the interval of thesynchronous signal field VFO I supposed to be T2.

The lock-in range on synchronization 300 after one repetition is theinterval T2 of the synchronous signal field VFO.

In the case after 100,000 times of repetition shown in FIG. 4c, at thebeginning of the guard data recording region 100, medium deterioration30 occurs for an interval of TC2. Accordingly, the guard data recordingfield 100 is shortened to an interval T5. However, only the guard datarecording field in which guard data is recorded is shortened, and thesynchronous signal field VFO necessary for synchronization is notinfluenced at all by the medium deterioration 30.

The lock-in range on synchronization 300 after 100,000 times as shown inFIG. 4d remains at T2 as in the initial state after one repetition.Hence, as in the initial state, a stable acquisition of synchronism isrealized.

In FIGS. 5a-d, the guard data in the guard data recording field is thesame as the recording pattern of the synchronous signal field VFO.Moreover, so as not to be discontinuous at the boundary of the guarddata recording field and synchronous signal field, the phase of therecording pattern is matched. FIG. 5a shows the data recording fieldafter one repetition, FIG. 5b shows the lock-in range onsynchronization, FIG. 5c shows the data recording field after 100,000times of repetition, and FIG. 5d shows the lock-in range onsynchronization after 100,000 times of repetition.

In the initial state after one repetition as shown in FIG. 5a, the guarddata recording field 100 at the record start point of the data recordingfield 5 is free from medium deterioration. The interval of the guarddata recording field in the initial state is supposed to be T1, and theinterval of the synchronous signal field VFO is supposed to be T2.

The lock-in range on synchronization 400 after one time of repetition isthus the sum T1+T2 of interval T1 of the guard data recording field andinterval T2 of the synchronous signal field VFO because the signal inthe guard data recording field is the same recording pattern as in thesynchronous signal field VFO and continuity is maintained. As comparedwith T2 of the lock-in range on synchronization 300 in the recordingpattern in which the signal of the guard data recording field isdifferent from the synchronous signal field VFO explained in FIGS. 4a-d,the lock-in range in the present embodiment is extended by the portionof the interval T1 of the guard data recording field.

In the case after 100,000 times of repetition shown in FIG. 5c, at thebeginning of the guard data recording region 100, medium deterioration30 occurs for an interval of TC2. Accordingly, the guard data recordingfield 100 is shortened to an interval T5. However, only the guard datarecording field in which guard data is recorded is shortened, and thesynchronous signal field VFO necessary for synchronization is not at allinfluenced by the medium deterioration 30.

The lock-in range on synchronization 400 after 100,000 times ofrepetition shown in FIG. 5d is the sum T5+T2 of interval T5 of the guarddata recording field 100 and interval T2 of the synchronous signal fieldVFO. As compared with T2 of the lock-in range on synchronization 300 inthe recording pattern in which the signal of the guard data recordingfield is different from the synchronous signal field VFO explained inFIGS. 4a-d, the lock-in range is extended by the portion of the intervalof the guard data recording field.

Accordingly, even if after 100,000 recording repetitions causing mediumdeterioration at the record start point, the lock-in range onsynchronization is longer than the interval T2 of the initialsynchronous signal field VFO by the portion of the interval T5 of theguard data recording field. As a result, stability and reliability of(phase locked loop (PLL) synchronization are improved.

As described herein, according to the present embodiment, by providingguard data in the guard data recording field 100 disposed between theheader field 4 and data recording field of the optical disc, with thesame recording pattern as in the synchronous signal field VFO, andkeeping continuity, the lock-in range on synchronization can be extendedbeyond the synchronous signal field VFO, and, therefore, if mediumdeterioration due to repeated recording occurs, the stability andreliability of acquisition of synchronism can still be maintained.

Embodiment 4

Referring now to FIG. 6, an optical disc device according to a fourthembodiment of the invention is described, which embodiment is intendedto record and reproduce by providing the recording pattern guard datarecording field at the beginning of a sector, the guard data being thesame as in the synchronous signal field VFO. Explanation is omitted forthe parts already described in the optical disc device in FIG. 19relating to the prior art described above.

What is added to the prior art is a VFO guard data generating circuit500 and a first record control circuit 201. The VFO guard datagenerating circuit 500 generates the same recording pattern in the guarddata recording field 100 and synchronous signal field VFO. The firstrecord control circuit 201 generates continuous gate timing so as not tocause any discontinuity between the guard data recording field 100 andsynchronous signal field 5b. As a result, in the guard data recordingfield 100 and synchronous signal field 5b, the same recording patternsfor synchronization are generated continuously.

To the beginning of the recording pattern generated in the VFO guarddata generating circuit 500, modulated data from the data modulationcircuit 13 is added. Such data timing is controlled by the first recordcontrol circuit 201. The combined data is provided to a laser drivingcircuit 12 in a later stage, and is recorded on the optical disc.

According to the present embodiment, as described herein, by adding theVFO guard data generating circuit 500 for generating common recordingpatterns in the guard data recording field 100 and synchronous signalfield VFO and the fist record control circuit 201 to the conventionaloptical disc device, the recording pattern for synchronization isrecorded in the guard data recording region 100 between the header field4 and synchronous signal field VFO, and, therefore, the lock-in range onsynchronization is extended beyond the interval of the synchronoussignal field VFO, so that an optical disc device enhanced in reliabilityand stabilization of acquisition of synchronism even in view of mediumdeterioration occurring due to repeated recording can be realized.

Embodiment 5

FIG. 7 is a step-by-step explanation of a recording method for anoptical disc according to a fifth embodiment of the present inventionfor recording and reproducing the same recording pattern in thesynchronous signal field VFO in the guard data recording field at thebeginning of a sector.

At step 210, the optical disc device reads the address information ofthe optical disc by a command from a host system in an address detectingcircuit 17 (see FIG. 6, for example). A system control circuit 18confirms whether an address of the sector is to be recorded or not.

At step 211, the record data is coded in a coding circuit 15, and ismodulated in a data modulation circuit 13 that outputs modulated data.

At step 212, to the beginning of the modulated data, a synchronoussignal VFO for synchronization is added by a VFO generating circuit 14.

At step 213, to the beginning of the synchronous signal VFO, guard datafor suppressing the effects of medium deterioration is added by a guarddata generating circuit 200.

Then, at step 214, in the corresponding sector to be recorded, therecord data generated at steps 211, 212, and 213 are controlled by thefirst record control circuit 201 and recorded in the proper order.Specifically, the guard data is recorded in the guard data recordingfield, and the synchronous signal VFO and user data are recorded in thedata recording field.

With these steps, the data can be recorded and reproduced in the opticaldisc in the recording format shown in FIG. 1.

Embodiment 6

Referring now to FIGS. 8a-d, an optical disc according to a sixthembodiment of the invention is described below, in which the recordinginterval of the guard recording field is changed at random in everyrecording.

In FIGS. 8a-d, the variable recording intervals of the guard datarecording field 100 in sectors 1, 2, 3, and 4, respectively, are shown.

In FIG. 8a, relating to sector 1, the recording interval of the guarddata recording field 100 is T1, and the interval of the succeedingsynchronous signal field VFO is T2. The combined interval of the guarddata recording field 100 and synchronous signal field VFO is T1+T2.

In FIG. 8b, relating to sector 2 next to sector 1, the recordinginterval of the guard data recording field 100 is extended by intervaldT compared to sector 1 to be T1+dT. The combined interval of the guarddata recording field 100 and synchronous signal field VFO is T1+T2+dT.It is understood that since the guard data recording field 100 isextended by dT, the terminal end of the data recording field is shiftedbackward by the same amount.

In FIG. 8c, relating to sector 3 next to sector 2, the recordinginterval of the guard data recording field 100 is extended by interval2dT compared to sector 1 to be T1+2dT. The combined interval of theguard data recording field 100 and synchronous signal field VFO is thusT1+T2+2dT. As the guard data recording field 100 is extended by 2dT, theterminal end of the data recording field is likewise shifted backward bythe same amount.

In FIG. 8d, relating to sector 4 next to sector 3, the recordinginterval of the guard data recording field 100 is T1, as in sector 1.The combined interval of the guard data recording field 100 andsynchronous signal field VFO is thus again T1+T2.

According to this scheme, in every recording, the recording interval inthe guard data recording field 100 is randomly changed in every sectorat a time resolution of dT. The number of bits for randomly changingthis time resolution dT is determined appropriately by the systemconfiguration. A specific example with respect to a phase change opticaldisc is given below.

When the channel bit frequency is 29.18 MHz, for the period t=34.27 nsecof one bit of the channel bit, supposing one byte of data corresponds to16 channel bits, 16 t=548 nsec is defined to be one byte in the data.The line velocity is about 6 m/s. The guard data recording field 100 ofinterval T1=20 bytes changes by 20 bytes+K (K=0 to 7), in eight types of0 to 7 bytes, at a resolution in the unit of one byte. By such randomtime shift, since the start point of the synchronous signal field VFOcan be changed at random, recording deterioration resulting from thesame recording pattern can be prevented. The recording interval of theguard data recording field is 20 bytes * 6 m/s * 548 nsec=66 μm.

Although not shown in FIGS. 8a-d, the random time shift is preferablyalso given to the guard data recording field 100 in which the recordingpattern is the same as in the synchronous signal field VFO. Accordingly,the length of gap field 7 is changed randomly in every recording. Forinstance, the gap field interval of 10 bytes (34 μm) is changed in 16ways corresponding to 0 to 15 channel bits, at the resolution in theunit of one channel bit t=34.27 nsec. This is described in detail later.

When using such random time shift, according to the relation between thenumber of times of recording and the deterioration interval in the guarddata recording field 100, the deterioration interval is 7 μm at 20,000repeated recordings, 10 μm at 50,000 repetitions, and 33 μm at 100,000repetitions.

As a result of employing random time shift, it is found that thedeterioration of the recording interval of the guard data recordingfield 100 is suppressed to 33 μm even if recording is repeated 100,000times. The recording interval of the guard data recording field 100 isset at 66 μm, and even after 100,000 times of recording, thedeterioration of the recording interval is not extended up to thesynchronous signal field VFO, so that the acquisition of synchronismremains stable.

Incidentally, since the recording pattern of the guard data recordingregion is identical to the synchronous signal VFO, the channel bitsrepeating as "00010001," and alternate repetition of mark and space inthe length of four channel bits on the recording medium may be employed.

Embodiment 7

Referring now to FIG. 9, an optical disc device according to a sixthembodiment of the invention is described, which is intended to recordand reproduce in an optical disc while randomly changing the recordinginterval of the guard data recording field in every recording.Explanation is omitted for the parts already described with respect tothe optical disc device in FIG. 19 relating to the prior art describedabove.

What is added to the prior art is a guard data generating circuit 200, afirst record control circuit 201, and a first random changing circuit220. The guard data generating circuit 200 generates specific guarddata. To the beginning of the guard data from the guard data generatingcircuit 200, a synchronous signal VFO from a synchronous signal VFOgenerating circuit 14 is added, and then modulated data from a datamodulation circuit 13 is added thereafter. The first random changingcircuit 220 changes the recording interval of the guard data recordingregion, by 20 bytes+K (K changing randomly from 0 to 7), at theresolution of 1 byte. While randomly changing the recording interval ofthe guard data recording field, the timing of the combined guard data,synchronous signal VFO and modulated data is controlled by the firstrecord control circuit 201, and these record signals are provided to alaser driving circuit 12 in a later stage, and recorded in the sectorson the optical disc while changing randomly in every recording.

As described herein, according to the present embodiment, by adding theguard data generating circuit 200 for generating guard data, firstrecord control circuit 201 and first random changing circuit 220 to theconventional optical disc device, the record start point is changedrandomly in every recording, and thus signal deterioration due torepeated recording of synchronous signal VFO and user data can besuppressed.

Embodiment 8

FIG. 10 shows a format structure of an optical disc according to aneighth embodiment of the present invention for recording and reproducingby randomly changing the length of first and second gap fields, andfirst and second guard data recording fields, in every recording, andsetting the changing amount of the first gap field smaller than thechanging amount of the first guard data recording field. Explanation isomitted for the parts already described in the format structure shown inFIG. 18 relating to the prior art described above.

What is added to the prior art is a mirror field 270 used to adjust aservo signal, a first gap field 271 of no-signal interval, a first guarddata recording field 272 for recording guard data, a second guard datarecording field 273 for recording guard data next to the data recordingfield 5, and a second gap field 274 of no-signal interval.

Herein, the recording interval of the first and second gap fields 271,274, and first and second guard data recording fields 272, 273 ischanged randomly in each sector in every recording.

FIG. 11 depicts an optical disc device for recording and reproducing inan optical disc by randomly changing the length of first and second gapfields, and first and second guard data recording fields, in everyrecording, and setting the changing amount of the first gap fieldsmaller than the changing amount of the first guard data recordingfield. Explanation is omitted for same parts already described withrespect to the optical disc device of FIG. 19 relating to the prior artdescribed above.

What is added to the prior art device is a guard data generating circuit200, a second record control circuit 230, a second random changingcircuit 240, and a polarity inverting circuit 250. The guard datagenerating circuit 200 generates specific guard data. To the beginningof the guard data from the guard data generating circuit 200, asynchronous signal VFO from a synchronous signal VFO generating circuit14 is added, and then modulated data from a data modulation circuit 13is added thereafter. The second random changing circuit 240 changesrandomly the recording interval of the first and second gap fields. Forexample, the first gap field is changed by 10 bytes+J/16 (J changingrandomly from 0 to 15) in every recording. Since the resolution of thechanging amount is J/16, one byte is composed of 16 bits in channelbits. The second gap field is changed by 25 bytes-J/16 (J changingrandomly from 0 to 15) in every recording. Accordingly, the total lengthof the recording interval of the first gap field and the recordinginterval of the second gap field is kept constant. Moreover, the secondrandom changing circuit 240 also randomly changes the recordingintervals of the first and second guard data recording fields. Forexample, the first guard data recording field is changed by 20 bytes+K(K changing randomly from 0 to 7, at the resolution of 1 byte.Similarly, the second guard data recording field is changed by 55bytes-K (K changing randomly from 0 to 7), at the resolution of 1 byte.Herein, the total length of the recording interval of the first guarddata recording field and the recording interval of the second guard datarecording field is also kept constant.

While randomly changing the recording interval of the first and secondgap fields and first and second guard data recording fields, the timingof the combined guard data, synchronous signal VFO, and modulated datais controlled in the second record control circuit 230. The recordsignal composed of these signals is passed to the polarity invertingcircuit 250 in a later stage, and the polarity of the record signal ischanged randomly in the sector interval in every recording. The recordsignal from the polarity inverting circuit 250 is provided to a laserdriver circuit 12, and the recording interval of the first and secondgap fields and the recording interval of the first and second guard datarecording fields are changed randomly, and the polarity of the recordsignal is changed randomly and is recorded in the sector on the opticaldisc.

Referring now to FIG. 12, a structural example of the second randomchanging circuit 240 is described. In FIG. 12, a random changing circuit701 is composed of 13 stages of shift registers 702, and is designed toreceive a clock 703 and a random update command 704. By the command ofthe random update command 704, the signal polarity and the changingamount are determined randomly by a one-bit signal 705 for determiningthe polarity of record signal, a four-bit signal 706 for determining thechanging amount of the first and second gap fields, and a three-bitsignal 707 for determining the changing amount of the first and secondguard data recording fields.

FIG. 13 is a flowchart showing the operation for rewriting the recordinformation of a sector by this optical disc device.

Referring also to FIG. 11, the operation is described below according tothe flowchart in FIG. 13.

At step 261, the optical disc device reads the address information ofthe optical disc by the command from a host system in an addressdetecting circuit 17. A system control circuit 18 confirms whether anaddress of a sector is to be recorded or not.

At step 262, the record data is coded in a coding circuit 15, and ismodulated in a data modulation circuit 13 that outputs modulated data.

At step 263, to the beginning of the modulated data, a synchronoussignal VFO for synchronization is added by a VFO generating circuit 14.

At step 264, to the first guard data recording field at the beginning ofthe synchronous signal VFO and the second guard data recording fieldconsecutive to the user data, guard data for suppressing the effects ofmedium deterioration are added by a guard data generating circuit 200.

At step 265, the changing amount of the recording interval of the firstand second gap fields is determined randomly by the changing amount of 0to 15 channel bits, at the resolution of one channel bit. Similarly, thechanging amount of the recording interval of the first and second guarddata recording fields is determined randomly by the changing amount of 0to 7 bytes, at the resolution of one byte. That is, by the extendedportion of the first gap field, the length of the second gap fieldbecomes shorter, and the total length is unchanged. Similarly, the totallength of the first and second guard data recording fields does notvary.

At step 266, while randomly changing the recording interval of the firstand second gap fields and first and second guard data recording fields,a record signal is created from the combined guard data, synchronoussignal VFO, and modulated data.

At step 267, it is determined whether to invert the polarity of therecord signal.

At step 268, if determined to invert the polarity at step 267, thepolarity of the record signal is inverted.

At step 269, the record signals determined in step 263 through step 268are recorded in the corresponding sectors to be recorded.

According to the above-described scheme, the signals are recorded in theoptical disc in the format as shown in FIG. 10.

The random changing state of the first and second gap fields and firstand second guard data recording fields is explained with reference toFIGS. 14a-d. FIGS. 14a-d depict a recording format in the sector byrandomly changing the length of the first and second gap fields andfirst and second guard data recording fields by the above method. On thesector of optical disc are formed an address signal 401, a first gapfield 402, a first guard data recording field 403, a record signal 404composed of synchronous signal VFO and user data, a second guard datarecording field 405, and a second gap field 406.

FIG. 14a shows a case in which the changing amount J of the first gapfield 402 is the minimum J=0, and the changing amount K of the firstguard data recording field 403 is the minimum K=0. Therefore, the lengthof the first gap field 402 is the minimum value of G1min, and the lengthof the second gap field 406 is the maximum value of G2max. The length ofthe first guard data recording field 403 is the minimum value of D1min,and the length of the second guard data recording field 405 is themaximum value of D2max. In the case shown in FIG. 14a, the record signal404 is located at the foremost position in the sector.

In FIG. 14b, J=Jmax and K=0, in FIG. 14c, J=0, K=Kmax, and in FIG. 14d,J=Jmax, K=Kmax. Herein, Jmax is the maximum changing amount of the gapfield, which is usually 15 channel bits, and Kmax is the maximumchanging amount of the guard field, which is usually 7 bytes. In thecase shown in FIG. 14d, the record signal 404 is located at the rearmostposition in the sector. The length of the first gap field 402 is themaximum value of G1max, and the length of the second gap field 406 isthe minimum value of G2min. The length of the first guard data recordingfield 403 is the maximum value of D1max, and the length of the secondguard data recording field 405 is the minimum value of D2min.

FIGS. 15a-b show schematic diagrams of deterioration of a sector. InFIG. 15a, J=0, K=0, and in FIG. 15b, J=Jmax, K=Kmax. As shown in thediagram, start end deterioration 501 occurs in the first guard datarecording field 403, and a start end deterioration region 504 is formedin a total length of the maximum changing amount Jmax portions of thefirst and second gap fields. Similarly, terminal end deterioration 502occurs in the second guard data recording field 405, and a terminal enddeterioration region 505 is formed in a total length of the maximumchanging amount Jmax portions of the first and second gap fields.However, this deterioration region is in the first and second guard datarecording fields, and further expansion of the start end and terminalend deterioration regions is prevented, and hence the deteriorationregion does not detrimentally affect the record signal 404 composed ofthe synchronous signal VFO and user data.

Incidentally, in the record signal 404 composed of the synchronoussignal VFO and user data, since the recording interval is randomlychanged and expanded at the resolution of one byte, the range 506 forinducing local oscillation is expanded, and the local deterioration 503is dispersed, so that the effects of local deterioration may bedecreased.

In actual recording operation, J is a channel bit, and one byte iscomposed of 16 channel bits, and K is a larger value as compared with J.Therefore, the positions of the first and second gap fields changerandomly and minutely, while the recording position changes ratherwidely in the record signal 404 enclosed by the first and second guarddata recording fields.

In this embodiment, J is set in channel bit unit, and K in byte unit, tosatisfy the following requirements. That is, the random shift of thefirst and second gap fields is small in scale so as not to expand thedeterioration region at the recording start and terminal end, and randomshift of channel bit in the minimum unit for handling digital data isrealized, whereas local deterioration is dispersed by increasing thechanging amount of the recording fields of the synchronous signal anduser data record signal, and the arrangement of information is simple.

The first and second guard data recording fields are intended to preventthe deterioration phenomenon occurring at the start and terminal end dueto repeated recording from propagating to the record signals such assynchronous signal VFO and user data. Therefore, from the viewpoint ofpreventing expansion of the deterioration region, the random shiftshould not be increased too much.

The local deterioration in record signals such as synchronous signal VFOand user data should be preferably dispersed by expanding the inductingregion by changing in byte unit, thereby lowering the possible rate ofeffects due to deterioration.

Usually, when handling digital data, it is preferred to handle the datain byte units. However, if the random shift is handled in the byte unitalone, deviation occurs in byte unit, and deterioration in byte unit islikely to occur, and therefore as compared with the random shift inchannel bit unit, the deterioration preventive effect of the medium isdecreased. On the other hand, if random shift is always handled inchannel bit unit only a fractional shift of 5 bits or 9 bits occurs, andsignal processing is difficult in reproduction.

In this embodiment, accordingly, the random shift in the first andsecond gap fields in no-signal interval is in channel bit unit, so thatdeterioration in byte unit can be prevented, and effects ofdeterioration in byte unit can be prevented, and effects ofdeterioration at start and terminal end of a sector can be effectivelysuppressed. In the record signals of synchronous signal VFO and userdata, if the random shift is handled in byte unit, the region to berecorded is expanded, and hence deterioration in mark unit can bedispersed, and, moreover, the data to be reproduced can be handled inbyte unit, so that no inconvenience is caused in signal processing inreproduction.

As a result, the recording position of record signal 404 of synchronoussignal VFO or user data as seen from the entire sector is changed overin two stages of random shift, that is, large random shift and smallrandom shift, in every recording. In the embodiment, for two types ofdeterioration, that is, deterioration at start and terminal end of asector and local deterioration occurring in every mark, effects of thesedeteriorations on recording and reproducing of information can beeffectively decreased.

Further according to the present embodiment, the polarity of the recordsignal is inverted randomly in every recording. FIGS. 16a-c shows therelation between the polarity of the record signal and the actualrecording state on an optical disc. In the sector of the optical discare formed an address signal 604, a first gap field 605, a first guarddata recording field 601, a record signal 607 composed of synchronoussignal VFO and user data, a second guard data recording field 608, and asecond gap field 609.

The record signal 601, if not inverted in polarity, is recorded in therecording medium in a state of 602, and if inverted in polarity, isrecorded in the recording medium in a state of 603. That is, byinverting the polarity, the non-fused portion and the fused portion ofthe foil forming a mark are completely opposite, so that a furthereffect is added to prevention of deterioration.

FIG. 17 is a diagram showing the result of an experiment confirming theeffect of random shift of the invention. In this experiment, afterrepeatedly recording the same data signals in the sector of the opticaldisc, the jitter values are shown. After recording repeatedly 100,000times, on the basis of the guideline of error probability of less thanonce in 10,000 times at the time of demodulation, the jitter value of15% or less is regarded as the standard of data reproduction.

In curve 50, the maximum changing amount of the first gap field isJmax=15 channel bits, and the maximum changing amount of the first guarddata recording field is Kmax=7 bytes, and in curve 51, the maximumchanging amount of the first gap field is Jmax=15 channel bits, and themaximum changing amount of the first guard data recording field isKmax=7 bytes, and polarity inversion is included.

As can be seen from curves 50 and 51, the desired conditions can besatisfied by the maximum changing amount of the first gap field ofJmax=15 channel bits, maximum changing amount of the first guard datarecording field of Kmax=7 bytes, and inclusion of polarity inversion.From the viewpoint of disc capacity, it is desired that the changingamounts of the first gap field and first guard data recording field beas small as possible, and hence it is judged that the combination ofmaximum changing amount of the fist gap field of Jmax=15 channel bits,maximum changing amount of the first guard data recording field ofKmax=7 bytes, and polarity inversion is preferred.

In the stage of the present experiment, incidentally, the random shiftwas Jmax=15 channel bits and Kmax=7 bytes, but, in the future, alongwith the technical progress such as development of high performancerecording thin film material, it is believed that the error probabilityrate may be lower than once in 10,000 times in demodulation after100,000 times of repeated recording even at a smaller shift width. Insuch a case, too, according to the invention, as in this embodiment, itis possible to suppress the effects of the deterioration phenomenon onthe accurate recording and reproducing of information at a certainlimited random shift amount.

Thus, according to the present embodiment, by randomly changing thelength of the first gap field and first guard field in every recording,and by inverting the polarity of record signal in every recording, atthe maximum changing amount of the first gap field of Jmax=15 channelbits, maximum changing amount of the first guard data recording field ofKmax=7 bytes, signal processing is facilitated in a limited random shiftamount, and effects of the two types of deterioration phenomenon inevery sector and in every mark on the accurate recording and reproducingof information can be suppressed.

In the present embodiment, by setting the recording pattern of guarddata in the first guard data recording field to the same recordingpattern in the synchronous signal field, and keeping continuous thephase of the record signal between the first guard data recording fieldand synchronous signal interval, the synchronous signal interval isexpanded, and system stability can be enhanced.

Moreover, in the optical disc device using the reproduced light outputand at least one type or more of recorded light output, regardless ofthe type of the recording medium, evidently, the invention can beapplied not only in the phase change optical disc, but also inmagneto-optical discs and others.

What is claimed is:
 1. An optical disc having a plurality of sectors,each one of said sectors, sequentially comprising: a first gap fieldwith a no-signal interval, a first guard data recording field forrecording guard data, a data recording field containing a synchronoussignal and following user data, a second guard data recording field forrecording the guard data, and a second gap field with a no-signalinterval, the total length of said first and second gap fields beingconstant, the total length of said first and second guard data recordingfields being constant, the length of said first and second gap fieldsand the length of said first and second guard data recording fieldsbeing randomly changeable in every recording, and the changing amount ofsaid first and second gap fields being smaller than the changing amountof said first and second guard data recording fields,wherein theresolution of the changing amount of said first gap field is a channelbit unit, and the resolution of the changing amount of said first guarddata recording field is a byte unit.
 2. An optical disc of claim 1,wherein the resolution of the changing amount of said first gap field is15 channel bits or less, and the resolution of the changing amount ofsaid first guard data recording field is 7 bytes or less.
 3. An opticaldisc device, operative on an optical disc having a plurality of sectorsdivided from a track, comprising:guard data generating means forgenerating guard data in first and second guard data recording fields;synchronous signal generating means for generating a synchronous signal;random changing means for (i) randomly changing the length of first andsecond gap fields with a no-signal interval in every recording, thetotal length of said first and second gap fields being constant, (ii)randomly changing the length of first and second guard data recordingfields in every recording, the total length of said first and secondguard data recording fields being constant, and (iii)controlling thechance amount of said first and second gap fields to be smaller than thechanging amount of said first and second guard data recording fields;and record controlling means for (i) forming each sector comprisingsequentially a first gap field with a no-signal interval, a first guarddata recording field for recording guard data, a data recording fieldcontaining a synchronous signal and following user data, a second guarddata recording field for recording guard data, and a second gap fieldwith a no-signal interval, and for (ii) recording signals in said firstand second guard data recording fields and said data recording fields,on the basis of the changing amount of said first and second gap fieldsand the changing amount of said first and second guard data recordingfields, wherein the resolution of the changing amount of said first andsecond gap fields is in the unit of channel bits, and the resolution ofthe changing amount of the first and second guard data recording fieldsis in the unit of bytes.
 4. An optical disc device of claim 3, whereinthe random changing means changes said first gap field by an amount of15 channel bits or less in every recording, and changes said first guarddata recording field by an amount of 7 bytes or less.
 5. A recordingmethod for an optical disc having a plurality of sectors divided from atrack, the method comprising the steps of:forming a sector structurecomprised sequentially of a first gap field with a no-signal interval, afirst guard data recording field for recording guard data, a datarecording field containing a synchronous signal and following user data,a second guard data recording field for recording the guard data, and asecond gap field with a no-signal interval; setting the total length ofsaid first and second gap fields constant, setting the total length ofsaid first and second guard data recording fields constant, whenrecording, randomly changing the lengths of said first and second gapfields and randomly changing the lengths of said first and second guarddata recording fields in every recording, controlling the change amountof said first and second gap fields to be smaller than the changingamount of said first and second guard data recording fields, furthercomprising setting the changing amount of said first gap field to aresolution unit of channel bits, and setting the changing amount of saidfirst guard data recording field to a resolution unit of bytes.
 6. Arecording method for an optical disc of claim 5, further comprisingsetting the changing amount of said first gap field to 15 channel bitsor less, and setting the changing amount of said first guard datarecording field to 7 bytes or less.